/*
 * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
 */
package com.opensource.dbhelp.dbutils.handlers;

import java.sql.ResultSet;
import java.sql.SQLException;

/**
 * <code>ResultSetHandler</code> implementation that converts one <code>ResultSet</code> column into a <code>List</code> of <code>Object</code>s. This class is thread safe.
 *
 * @param <T>
 *            The type of the column.
 * @see com.opensource.dbhelp.dbutils.ResultSetHandler
 * @since DbUtils 1.1
 */
public class ColumnListHandler<T> extends AbstractListHandler<T> {

	/**
	 * The column number to retrieve.
	 */
	private final int columnIndex;

	/**
	 * The column name to retrieve. Either columnName or columnIndex will be used but never both.
	 */
	private final String columnName;

	/**
	 * Creates a new instance of ColumnListHandler. The first column of each row will be returned from <code>handle()</code>.
	 */
	public ColumnListHandler() {
		this(1, null);
	}

	/**
	 * Creates a new instance of ColumnListHandler.
	 *
	 * @param columnIndex
	 *            The index of the column to retrieve from the <code>ResultSet</code>.
	 */
	public ColumnListHandler(int columnIndex) {
		this(columnIndex, null);
	}

	/**
	 * Creates a new instance of ColumnListHandler.
	 *
	 * @param columnName
	 *            The name of the column to retrieve from the <code>ResultSet</code>.
	 */
	public ColumnListHandler(String columnName) {
		this(1, columnName);
	}

	/**
	 * Private Helper
	 * 
	 * @param columnIndex
	 *            The index of the column to retrieve from the <code>ResultSet</code>.
	 * @param columnName
	 *            The name of the column to retrieve from the <code>ResultSet</code>.
	 */
	private ColumnListHandler(int columnIndex, String columnName) {
		super();
		this.columnIndex = columnIndex;
		this.columnName = columnName;
	}

	/**
	 * Returns one <code>ResultSet</code> column value as <code>Object</code>.
	 * 
	 * @param rs
	 *            <code>ResultSet</code> to process.
	 * @return <code>Object</code>, never <code>null</code>.
	 * @throws java.sql.SQLException
	 *             if a database access error occurs
	 * @throws ClassCastException
	 *             if the class datatype does not match the column type
	 * @see com.opensource.dbhelp.dbutils.handlers.AbstractListHandler#handle(java.sql.ResultSet)
	 */
	// We assume that the user has picked the correct type to match the column
	// so getObject will return the appropriate type and the cast will succeed.
	@SuppressWarnings("unchecked")
	@Override
	protected T handleRow(ResultSet rs) throws SQLException {
		if (this.columnName == null) {
			return (T) rs.getObject(this.columnIndex);
		} else {
			return (T) rs.getObject(this.columnName);
		}
	}

}